The present invention relates to monitor circuit arrangements for monitoring the energization of an energizable unit connected for controlled switching of energy supplied from an alternating voltage supply source.
A plurality of circuit arrangements of the kind to which the invention relates may be employed in a conflict monitor system for monitoring the alternating voltage mains supply energization of individual lamps or groups of lamps of a traffic signal system. In such an arrangement, energy is supplied to the lamps via controlled switching devices. If such a switching device is faulty, it is possible for the switching device to function as a half-wave rectifier. A signal lamp will still glow if energized by half-wave rectified current and it is therefore desirable for a conflict monitor to indicate energization of two lamps under conditions when the respective lamps are supplied with current on alternate half-cycles of the supply and supplied in anti-phase with each other so that consequently a voltage is not present across both lamps simultaneously. In contrast to the foregoing, in circumstances when the level of energization of a lamp is insufficient for the lamp to glow, it is undesirable to provide an indication of energization even though a voltage is present across the lamp.